The present invention relates to a substantially improved color-developer composition for use in recording sheets. More particularly, the present invention is directed to a pressure-sensitive record sheet material which comprises a supporting web containing a coating composition adhered thereto, said coating composition exhibiting enhanced color and enhanced fade resistance when reacted with normally colorless chromogenic compounds.
A record member, as the term is used in describing this invention, comprises a base sheet or web member either of fibrous construction, such as paper, or of continuous structure, such as films of organic polymeric material, carrying the color-reactant particles in an exposed state with respect to applied ink. Particles of the coating composition of this invention are arranged in intimate juxtaposition to form an apparently unbroken ink-receptive surface, yet substantially each particle individually is available for contact with applied ink. While the record member is adapted to receive any kind of ink, whether colored or colorable, its special utility is its use with an oily ink which is normally colorless or only slightly colored and carries in liquid solution a colorless chromogenic reactant having the property of becoming colored upon contact with an acidic composition.
During the last decade, one of the most prominent of such colorless recording systems utilized a coloring principle in which an oily ink having included therein chromogenic reactants, normally colorless, was used on an ink-receiving sheet sensitized with substantially oil-soluble acid reactants, such as phenolic resins, or insoluble acid-like materials of high surface activity, such as attapulgite and zeolite material. As the normally colorless chromogenic material content of inks used therewith, the most outstanding is Crystal Violet Lactone which in the colored form has intense hue in the blue end of the visual spectrum band. Such systems are disclosed in U.S. Pat. No. 2,712,507, which issued July 5, 1955, on the application of Barrett K. Green, and in U.S. Pat. No. 3,672,935, which issued June 27, 1972, on the application of Robert E. Miller, et al, and pertain to constructions in which the ink is applied from an oversheet by pressure release from microscopic capsules. These systems are now in world-wide use and command a predominant position in the field of colorless recording systems, and their continued use is expected.
As distinguished from pigment inks, the chromogenic material in the colorless ink of these systems is in the nature of a colorless dye or combination of dyes that assume, through chemical reaction, a visually distinctive color when undergoing reaction with the acid reactant on the sheet.
For most recording purposes, it is essential from a commercial standpoint that a distinctively colored mark make prompt appearance on the application of colorless ink to the recording surface to produce a visible representation of whatever is meant to be recorded, that the color be of distinctive hue but also of high intensity, and that the mark remain colored for a long period of time consistent with the objective of permanent recording. The well-known infirmities of colored dyes as regards permanence relate to light fading, thermal fading, and molecular rearrangements and disintegrations of various kinds in which part or all of the visually perceptible color is lost.
Accordingly, it is an object of the present invention to provide a color-developer composition which is used in the preparation of recording sheets, said color-developer composition exhibiting enhanced color and enhanced fade resistance.
Another object of the present invention is to provide a color-developer composition for use in carbonless copy paper record materials which produce developed prints that are more resistant to fade than any of those developed by the known prior art systems.
A further object of the present invention is to provide a developer composition for use in carbonless copy paper record materials which give developed prints that are more intense when freshly developed compared to those developed by known resinous systems.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Pursuant to the present invention, it has been found that an improved coating composition which exhibits enhanced color and enhanced fade resistance when reacted with normally colorless chromogenic compounds can be produced by utilizing specific phenol-formaldehyde resins with a specific metal in its oxide or hydroxide form in the color developer composition. Thus, the present invention achieves a substantial improvement in color response of specific resins by the addition of a specific metal thereto.
The particular phenol-formaldehyde resins which are effective in achieving the improved color response as defined by the present invention are zinc-modified alkylphenol-formaldehyde resins wherein the alkyl group contains 8 or 9 carbon atoms. These alkylphenol-formaldehyde resins include zinc-modified para-octylphenol-formaldehyde resin and zinc-modified para-nonylphenol formaldehyde resin. The preferred zinc-modified alkylphenol-formaldehyde resin of the present invention is para-octylphenol-formaldehyde resin, hereinafter referred to as the Zn-POP resin. The zinc-modified alkylphenol-formaldehyde resins utilized in the present invention can be made much in the manner of the zinc-modified phenolformaldehyde novolak resins as described in U.S. Pat. No. 3,737,410.
The specific metal compound which is utilized in the developer composition of the present invention is either calcium oxide, calcium hydroxide or magnesium oxide. Thus, it is the specific use of both the zinc-modified alkylphenol-formaldehyde resin and either calcium oxide, calcium hydroxide or magnesium oxide in the developer composition which is effective in producing a developer composition used in carbonless copy paper record materials which produce developed prints which are more intense and resistant to fade when compared to prior art resinous systems. Thus, metal oxides and hydroxides other than calcium oxide, calcium hydroxide and magnesium oxide, when utilized together with the above-mentioned resins, do not produce the advantageous results as defined by the present invention. Even metals which are in the same group of the Periodic Table as calcium and magnesium, for example barium, when used in either oxide or hydroxide form together with the above zinc-modified alkylphenol-formaldehyde resins, do not achieve the improvements in print intensity and fade resistance as defined by the present invention. Calcium oxide and calcium hydroxide have been found to produce particularly desirable results.
In still a further advantageous feature of the present invention, it has been found that particularly desirable results are achieved when the calcium oxide, calcium hydroxide or magnesium oxide is present in an amount of about 0.5 to 6% by dry weight based upon the dry weight of the total developer composition, preferably about 1 to 4% by dry weight.
In addition of the zinc-modified alkylphenol-formaldehyde resins and either calcium oxide, calcium hydroxide or magnesium oxide, a typical developer composition would include such materials as kaolin clay, silica gel, calcium carbonate, and various binders, such as for example, styrene-butadiene latex binder and cooked starch binder.
Kaolin is generally known and used in the paper-making industry as "China Clay" and is outstandingly preferable as the particulate oil-insoluble and water-insoluble material for improving the printing quality of the paper. A white kaolin is used and, because of its whiteness, its plate-like particle form, which gives it unparalleled coating properties in aqueous slurries, its universal abundance in supply, its historical general usage in the paper-making and paper-converting industries and its low cost, it is an ideal material. Of course, there are many other materials of a mineral nature which can be used instead of and matched against kaolin clays as the standard of perfection. Other types of materials such as bentonites can be utilized, although they are not as good as kaolin from a rheological standpoint and from the standpoint of printing quality.
From the foregoing choice of materials, a number of different specific compositions on a dry basis can be made, and these may then be used as desired, as being made into an aqueous slurry to be coated on a finished paper sheet, to be applied to a wet sheet of paper in the formative state in any desired manner, or made a part of the paper finish from which a paper sheet is made, or on the other hand, applied as a dispersion coating to a continuous film-like web such as synthetic organic polymeric material made into record sheets, bands, or strips, or to any record support material surface, all coming within certain limits merely set as practical and not set for any chemical or physical reason. In general, so as to be economical, the materials should be used in just sufficient quantities to make useful records for the purpose in view, and this relates to criteria of the factors of intensity, definition, color, and a great many other factors with regard to the characteristics of the base web material, the characteristics of the ink to be applied, and the environment of use, all of which come within the paper manufacturers' and printers' skill and general knowledge and are not deemed to be of inventive or operative significance, but following and employing the inventive concept. Generally, but not as a limitation in any sense, an aqueous dispersion of the particulate materials could well be from 30% to 70% water, by weight, and the remainder from 70% down to 30% being solid reactants. Amounts of paper-coating adhesives are added as is necessary to adhere the particles to the base web to which it is applied, but, of course, adhesives that have a tendency to mask the particles physically should not be used, nor should any material be used as an adhesive in great excess of actual requirements, all of such factors tending to decrease the efficient use of the associated active particles because of a limitation of the exposed surface area. Here again, the paper makers' and printers' skill and judgment play a part.
If desired, some attapulgite or zeolite material may be used with the polymeric material and kaolin clay, and it is within contemplation that other materials of reactant nature can be employed to supplement the main reactant, for specific purposes. In this area of permissible substitutes or addition materials, silica gel has considerable standing because it is capable of instantaneously strongly coloring oil solutions of normally colorless chromogenic materials and is an efficient oil receptor for oil-base ink. Where the particles of kaolin and acid polymeric material are slightly delayed in responsiveness because of their physical situation or condition in the support sheet, an amount of silica gel up to equal the amount of acid polymeric material may be used for its beneficient effect in the characteristic states, but such use is not necessary to the practice of the invention in its simplest form. Silica gel is oil-insoluble but absorbent thereof, may be finely ground, is colorless, disperses readily in water, and may be treated to increase its porosity and effectiveness as an acid. The polymeric-material-produced color of normally colorless chromogenic material is significantly more persistent than that produced by silica gel, and this must be considered in the use of the latter material.
The particle size of the reactants preferably should be from 1 to 3 microns in largest dimension, although considerable latitude at the expense of efficiency and economy is tolerable. For instance, if the grinding of materials to the most effective size is too expensive, their larger sizes are tolerable as long as sufficient color reaction per unit area of the record material is provided. On the other hand, finer grinding may result in more efficient use of materials on a weight basis, if not on a cost basis, and a lighter weight finished sheet may thereby be produced.
One of the chief considerations in selecting a preferred embodiment of the present invention must be concerned with the manufacture of the record sheet, and as of now one of the best ways to sensitize a sheet is to apply an aqueous slurry of the novel composition to a finished web of paper as it passes the coating station in a paper-making machine. Such a coating composition contains binder material and may contain defoamers and dispersing agents common to paper-coating practices, but their specification in no way is to mean a limitation of the practice of the invention in regard to either choice or necessity.
The binders which can be utilized in the developer composition of the present invention include gum arabic, ethyl cellulose, nitrocellulose, styrene-butadiene latex, and the like. The resinous particles are commonly bound to paper with cooked starch binder and latex binders such as styrene-butadiene latexes.